1. Field of the Invention
The present invention relates to a laser shock processing operation, and, more particularly, to a method and apparatus for modifying a workpiece previously subjected to a laser shock processing treatment, such as by removing material from, or adding material to, the laser shock processed region.
2. Description of the Related Art
The use of laser shock processing has found wide success, particularly in applications involving the enhancement of certain structural features such as the leading and trailing edges of airfoils in integrally bladed rotor systems. However, the high levels of compressive residual stresses that accompany laser shock processing may at times produce unique features in a processed workpiece. Recognition of the occurrence of one or more of these features has underpinned various efforts to examine the extent to which such processing can be modified to mitigate or remove these features, if they prove to be undesirable in a particular application.
Laser shock processing can leave surface geometry irregularities such as surface roughness and partially rolled-over or extruded edges, and other undesirable features. The surface roughness may, for example, take the form of laser-beam-spot depressions, surface melt or ‘staining’, pits from collapsed sub-surface porosity in castings, and beaded surface patterns. The surface roughness created by laser shock peening can vary from none to 0.001 to 0.002 inches in depth. Surface roughness as little as 0.0005 inches is a concern in certain applications such as airfoils, or polished surfaces. Laser shock peening may also cause some distortion in the shape of the part due to the compressive residual stresses created. This may necessitate smoothing the surface of airfoils of aircraft gas turbine engine blades and integrally bladed rotors (IBRs) after laser peening or shot peening at high intensities. This may be desirable to increase the aerodynamic efficiency of the airfoils after processing. In addition, the performance of some parts is degraded by required manufacturing steps, for example, certain machining operations that leave a rough surface, or intensive shot peening.
In view of the foregoing, there is needed a material treatment process that eliminates undesirable distortion and surface roughness introduced by conventional manufacturing processes or laser shock processing, without sacrificing the benefits of such processing.